A Pilot Study of Suvorexant for Insomnia in Parkinson Disease

Inclusion Criteria: * Has signed and dated an Institutional Review Board-approved informed consent form before any protocol-specific screening procedures are performed; * Has a diagnosis of Parkinson disease according to the United Kingdom Parkinson Disease Society Brain Bank Criteria; * Has a modified Hoehn and Yahr Stage of 1-3, inclusive; * Is aged 30-80 years old, inclusive; * Has had no change in Parkinson's Disease medications during the 4 weeks preceding screening, with no dose changes during the study, except that as needed doses of carbidopa/levodopa will be allowed to address periodic worsening of parkinsonian symptoms; * Is willing and able to complete polysomnogram; * Is subject willing and able to limit alcohol use to 1 alcoholic drink per day during the study period and abstain from alcohol for 6 hours prior to each study-related polysomnogram? * Is subject willing and able to abstain from caffeine and marijuana for 6 hours prior to and during each study-related polysomnogram * Is subject willing and able to abstain from products containing nicotine during each study-related polysomnogram? * Has Insomnia Disorder defined by diagnostic criteria published in the Diagnostic and Statistical Manual of Mental Disorders, 5th edition; namely, subject report of all of the following: * One of the following: difficulty initiating sleep; difficulty maintaining sleep; or early morning waking; * Sleep disturbance causes clinically significant distress or impairment in social, occupational, educational, academic, behavioral, or other important areas of functioning; * Sleep difficulty has occurred on 3 or more nights per week; * Sleep difficulty has been present for at least the past 3 months; * Sleep difficulty occurs despite adequate opportunity for sleep; * Insomnia is not explained by another sleep disorder; * Insomnia is not attributable to physiological effects of a consumed substance; * On screening polysomnogram, has a latency to persistent sleep \> 20 minutes OR total wakefulness after sleep onset \> 45 minutes; * May use other medications that could influence sleep, other than those specifically prohibited, as long as the dose is stable for 4 weeks preceding screening, with no dose changes during the study; and * Has valid health insurance coverage at the time of study enrollment and expects this coverage to remain valid for the duration of the study period. Exclusion Criteria: * Is a woman who is breast-feeding, pregnant, or has the potential to become pregnant during the course of the study (fertile and unwilling/unable to use effective contraceptive measures); * Does subject have an implanted deep brain stimulator? * Has a history of narcolepsy; * Has a diagnosis of severe chronic obstructive pulmonary disease, defined by forced expiratory volume in 1 second \< 50% of predicted on most recent available pulmonary function test (a pulmonary function test is not required if the subject has never been diagnosed with chronic obstructive pulmonary disease); * Has a history of severe obstructive sleep apnea or evidence of severe obstructive sleep apnea on screening polysomnogram, with severe obstructive sleep apnea defined as having an apnea-hypopnea index \> 30; * Is concurrently using other central nervous system depressants, including alcohol, except that one alcoholic drink per day will be allowed for those with normal hepatic function provided the drink is consumed at least 2 hours prior to or 8 hours after taking the study drug, and no alcohol will be permitted for 24 hours before polysomnogram visits; * Is concurrently using digoxin; * Is concurrently using any moderate or strong inhibitor of cytochrome P450 3A; * Is concurrently using any strong inducer of cytochrome P450 3A; * Has evidence at screening of severe hepatic impairment as defined by a Child-Pugh score \> 10; * Has evidence at screening of severe cognitive impairment as defined by a Montreal Cognitive Assessment score \< 15, or has cognitive impairment that in the opinion of the investigator would prevent completion of study procedures or the ability to provide informed consent. * Has evidence at screening of suicidal ideation in the past 6 months as defined by a positive response to any one of Questions 2-5 on the Columbia Suicide Severity Rating Scale or of a lifetime history of suicidal behavior as defined by any positive response to the suicidal behavior section of the Columbia Suicide Severity Rating Scale.